[KF5] Add a variant of KFilePlacesModel::closestItem that can keep hidden items

As discussed in 74904f0c which changed the behavior from never skipping hidden entries to always.

In KF6 this change will be made adding an optional arg instead of new method: !1415 (closed)

We want to backport this to KF5 because it causes BUG: 461872 in KDE Connect.